Semi-circular flap gate as a flow metering structure in circular channels

Abstract

This research proposes slit and solid semi-circular flap gates for discharge measurement along the circular channels under free flow condition. A top-hinged flap gate deflects by flowing water against its weight due to the flow hydrodynamic forces. The deflection angle of the semi-circular flap gate can be considered as either independent variable or dependent variable. Two models are proposed for the stage-discharge relation based on the Buckingham's theorem of dimensional analysis. The first model considers the deflection angle as an independent variable while the second model considers it as a dependent variable. A series of laboratory experiments (254 runs) were performed to investigate the flow process of slit and solid semi-circular flap gates located along of two horizontal, circular pipes. Using the data collected from two pipes of nominal diameters 20 and 30 cm, the proposed models were calibrated. The first model has an average error less than 2.5%, while the second general model has an average error about 2.55%, thus actual discharge through the circular channels can be accurately estimated using the proposed stage-discharge equations. The results showed that viscosity effects are significant in second model, while these effects are important in first model only for slit flap gates. The proposed inline flap gate offers a simple and reliable discharge measurement approach with acceptable accuracy.